Modulator



July 11, 1950 PAwLEY 2,514,413

MODULATOR Filed Sept. 19} 12545 2 Sheets-Sheet 1 LOAD A-C POWER INPUTSTORAGE O 0- DEVICE -A-C POWER LOAD INPUT gwua/wto'a MYRON G. PAWLEY y1950 M. e. PAWLEY ,51

MODULATQR Filed Sept. 19, 1945 2 Sheets-Sheet 2 ILE=E in I o '2 '00(VOLTAGE INDUCED m wmnms n) IIE=3 0| (THYRATRON PLATETO GATHODE VOLTAGE)(THYRATRON CRITICAL emu VOLTAGE) l I, HYRATRON FIRES ,1 AT THIS TIME o2(THYRATRON GRID-TO- CATHODE VOLTAGE) THYRATRON FIRES AT THlS TIME [O4(VOLTAGE APPLIED TO LOAD) MYRON G. PAWLEY @R MW energy in shortintermittent bursts.

Patented July 131, 1950 MODULATOR Myron G. Pawley, Alexandria, Va.

Application September 19, 1945, Serial No. 617,413

6 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) This invention relates to pulse generators, and isparticularly directed to providing simple apparatus suitable foremployment as the modulater in an echo-ranging or other pulse-modulatedradio system.

The function of the modulator component in such systems is to produce aseries of highpower, short-duration voltage pulses for application to ahigh frequency radio transmitter, to cause the transmitter to emit radiofrequency The invention herein described has a simpler circuit andrequires less apparatus to accomplish the required result thanpre-existing modulator systems, and is thus particularly adapted for usein echo-ranging systems wherein small size, light weight, and economyare important design considerations.

An object of this invention is to provide a simple, light weightmodulator for echo-ranging systerns.

Another object of this invention is to provide a modulator, suitable foremployment in pulsemodulated radio systems, which requires fewcomponents and is inexpensive.

The invention will be described with reference to the appended drawings,of which:

Figure 1 is a circuit diagram in schematic and block form, of anillustrative embodiment of the invention;

Figures 2, 3 and 4 are voltage-time graphs showing the variation withtime of various voltages involved in the operation of the embodiment ofthe invention illustrated in Figure 1; and

Figure 5 is a diagram, in schematic and block form, of still anotherembodiment of the inven tion.

Referring to Figure 1, transformer i0 is a stepup power-transformer, ofwhich primary winding l is connected to an A.-C. power source. In atypical application the power source might supply energy at 115 volts,400 cycles per second. One side of high voltage secondary winding II isgrounded; the other side is connected through inductor [2 to oneterminal of energy storage device l3. Device I3 may be a simplecondenser or it may be a pulse-forming network comprising capacitanceand inductance. In either event, the impedance of device I3 ispredominantly capacitive to currents of low frequency such as that ofthe power source. The other terminal of storage device I3 is connectedto the cathode of grid-controlled gas tube 20 and is returned to groundthrough resistor l5. Gas tube 20 is of the type commonly calledthyratron" and has the grid thereof connected to ground through limitingresistor I 7. Primary winding 2 of step-up pulse transformer 30 isconnected between the plate of gas tube 20 and the junction of device I3and inductor 12. The secondary winding 33 of pulse transformer 30 isconnected across load device 25, shown in block form. In a practicalapplication load 25 might be the power input terminals of a magnetronoscillator or other high frequency radio transmitter.

The secondary loop comprising winding l I and storage device I3 isadjusted to be resonant at the power frequency, and for this purpose itmust contain a substantial amount of inductance. The required inductanceis represented in Figure l as inductor 12. in practice inductor l2 maybe a physical coil, it may be the leakage inductance of winding ll, ifthat be adequate, or it may be reflected inductance in the secondaryloop produced by a physical inductor inserted in the primary circuit oftransformer Ill.

The system operation may best be described with reference to Figures 2,3, and 4. All these figures are graphs in Cartesian coordinates havingtime as abscissa and voltage as ordinate. The horizontal time scales areidentical for the three figures, but the vertical scales, indicatingvoltage. are in no case calibrated numerically and no uniformity ofscale from one figure to another is intended. Curve I00 on Figure 2shows, for time reference purposes, the voltage across secondary windingll, polarity taken with reference to the grounded side thereof. Figure 3contains three curves showing the approximate conformation of thevoltage waveforms for thyratron gas tube 20. Curve l0l represents thevoltage at the plate of gas tube 20 relative to its cathode; curve 802represents the voltage of the grid of tube 20 relative to cathode; curveI02 represents the voltage of the grid of tube 20 relative to cathode,and curve I03 represents the instantaneous value of the grid-cathodevoltage required for ionization, the so-called firing voltage. Curve I04on Figure 4 shows graphically the waveform of the high-pow ered outputvoltage pulses supplied to the load. On the time scale employed forFigures 2, 3, and 4, the duration of the output pulses-a fewmicroseconds or less-is imperceptible. The positive polarity shown forthe pulses in Figure 4 is arbitrarily chosen; either positive ornegative pulses can be had at will by reversing the connections toeither winding of pulse transformer 30.

During the positive half cycles of voltage across the secondary winding,as indicated by curve I00 starting at zero time, current fiows in adirection to charge storage device I3 in a polarity such that itsnegative terminal is that connected to the cathode of gas tube 20.Winding 3 of pulse transformer 30 has no drop across it except when gastube 20 is conducting; consequently during this interval the plate oftube 20 becomes increasingly positive relative to its cathode, asstorage device I3 charges. This voltage rise is shown graphically bycurve IOI, starting at zero time.

During the same part of the cycle the charging current through resistorI5 raises the cathode of gas tube 20 above ground potential and thusproduces a negative-grid-to-cathode bias voltage as shown by curve I02.At the instant marked t1, on the time scale, when storage device I3 isapproximately at peak charge, the grid-cathode voltage of tube 20 risesto a point more positive than the gas tubes firing voltage. Thisphenomenon is represented graphically by the intersection of curves I02and I03. At that instant, the gas in tube 20 ionizes and the tubebecomes virtually a short-circuit. As a result the entire voltage builtup across storage device I3 is suddenly applied to the primary winding 3of pulse transformer 30. A voltage several times larger instantlyappears across the secondary winding 33 and is applied to load 25. Thepulse of voltage continues until storage device I3 has dischargedvirtually all its stored energy. When this has occurred gas tube 20deionizes and becomes again an open circuit.

The waveform and duration of the output pulse produced are dependentupon the impedance of the load, the constants of the pulse transformer,and the characteristics of the storage device. The leading edge of thevoltage pulse will in any event be very steep, and in most cases thetrailing edge will likewise have a large slope. In general apulse-forming network employed as a storage device will give a morenearly rectangular output pulse than will a simple condenser in the samerole. In practical constructions output pulses having a duration of onemicrosecond or less have been obtained without difiiculty.

When the stored energy in storage device I3 has been dissipated inproducing the output pulse and gas tube 20 has deionized, the voltagefrom the power transformer starts the negative part of its cycle (theinterval t1 to t: on the time axes). Current flows around the secondaryloop in a direction to charge storage device I3 negatively and to makethe grid of gas tube 20 positive relative to its cathode. During thispart of the cycle, the plate of tube 20 is negative, as shown by curveIN, and the gas tube grid voltage flattens out at a value slightly abovezero relative to cathode. The voltage drop in grid-current limitingresistor I'I maintains the grid at approximately cathode potentialduring the entire part of the cycle in which there is a flow of gridcurrent.

At time 152 the source voltage again reverses, and, aided by the storedcharge'in device I3, begins to force current around the circuit in theoriginal direction. This results in storage device I3 again becomingcharged positively, developing a very high positive plate voltage on thegas tube, as before. At time is the grid voltage again rises above thecritical value, the gas tube fires, and another output pulse isproduced. This cycle of events continues indefinitely, one output pulsebeing produced for each cycle of source voltage.

An alternative embodiment of the invention is shown in schematic andblock form in Figure 5. In this embodiment the power transformer I0 isdesigned to possess sumcient secondary leakage inductance to effectresonance in the secondary loop; hence no counterpart to inductor I2 ofFigure 1 appears in Figure 5. The primary winding I2I of powertransformer I I0 is, as in the previous embodiment, connected to anA.-C. power source. One side of secondary winding III is connected tothe plate of grid-controlled gas tube I20 which is of the same type astube 20 of Figure 1; the other side of winding III is grounded. ResistorH5 is connected between the cathode of tube I20 and ground; resistor II1 is connected between the grid of tube I20 and ground. Storage deviceI I3, which may be a condenser or a pulse-forming network, is connectedin series with primary winding I 23 of pulse transformer I30 between theplate and cathode of gas tube I20. Secondary winding I33 of the pulsetransformer I30 is connected to load device I25, which may in practicebe a high frequency radio transmitter.

The operation of this embodiment is identical in principle to that ofthe embodiment already described. The resonant charging path compriseswinding II I, with its leakage inductance, resistor H5, storage deviceH3, and the primary winding I23 of the pulse transformer.

The voltage on the gas tube grid varies as a function of the chargingcurrent, just as in the other circuit, and the gas tube fires when thecharge stored in device II3 nears its peak. The ionization of the gastube impresses the entire voltage of storage device II3 across the pulsetransformer primary, and the output pulse results.

The rearrangement of parts resulting in the storage device. chargingthrough the pulse transformer primary does not appreciably affect theoperation of the modulator or alter the voltage Waveforms, because therate of change of current through winding I23 during the chargingprocess is much too slow to produce any appreciable induced voltageacross the load. The circuit of Figure 5 possesses the advantage overthe first circuit described that no part of the pulse transformer is ata high potential above ground except during the short intervals when theoutput pulses are being produced. This may induce insulationdifiiculties in practical installa- It will be understood that theembodiments of the invention herein shown and described are exemplaryonly and that the scope of the invention is to be determined byreference to the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination, an alternating-current power source; charge storagemeans and a resistor connected in closed series connection with thepower source; a grid-controlled, gas-filled rectifier tube having a.cathode, an anode, and a grid; load means; means connecting the gas tubeand the load means in a series connection with the storage means; andmeans connecting the grid and cathode of said tube across said resistorso that the charging current in the resistor is operative to bias thegrid negatively relative to the cathode to maintain the gas tubenonconducting while the storage means is charging and to fire the gastube when the charge in the storage means is maximum, therebydischarging the storage means into the load.

2. In combination, an alternating-current power source; inductancemeans, charge storage means, and a resistor connected in closed seriesconnection with the power source; a grid-controlled, gas-filledrectifier tube having a cathode, an anode, and a grid; load means; meansconnecting the gas tube and the load means in a series connection withthe storage means; and means connecting the grid to the power circuit ata point operative to cause charging current in the resistor to bias thgrid negatively relative to the cathode to maintain the gas tubenonconducting while the storage means is charging and to fire the gastube when the charge in the storage means is maximum, therebydischarging the storage means into the load.

3. In combination, an alternating-current power source; inductancemeans, charge storage means, and a resistor connected in closed seriesconnection with the power source substantially resonant at the frequencyof the power source to form a circuit; grid-controlled, gas-filledrectifier tube having a cathode, an anode, and a grid; load means; meansconnecting the gas tube and the load means in a series connection withthe storage means; and means connecting the grid to the power circuit ata point operative to cause charging current in the resistor to bias thegrid negatively relative to the cathode to maintain the gas tubenon-conducting while the storage means is charging and to fire the gastube when the charge in the storage means is maximum, therebydischarging the storage means into the load.

4. In combination, an alternating-current power source; a powertransformer having primary and secondary windings; means connecting theprimary winding to the power source; charge storage means and a resistorconnected in closed series connection with the secondary winding; loadmeans; a pulse transformer having primary and secondary windings; meansconnecting the load means to the secondary winding of the pulsetransformer; a grid-controlled gas-filled rectifier tube having acathode, an anode, and a grid; means connecting the gas tube in a seriesconnection with the primary winding of the pulse transformer and thestorage means; and means connecting the grid and cathode of said tubeacross said resistor so that the charging current in the resistor isoperative to bias the grid negatively relative to the cathode tomaintain the gas tube non-conducting while the storage means is chargingand to fire the gas tube when the charge in the storage means ismaximum.

5. In combination, an alternating-current power source; a powertransformer having primary and secondary windings; means connecting theprimary winding to the power source; inductance means, charge storagemeans, and a resistor connected in closed series connection with thesecondary winding to form a circuit substantially resonant at thefrequency of the power source; load means; a pulse transformer havingprimary and secondary windings; means connecting the load means to thesecondary winding of the pulse transformer; a grid-controlled,gas-filled rectifier tube having a cathode, an anode, and a grid; meansconnecting the gas tube in a series connection with the primary windingof the pulse transformer and the storage means; and means connecting thegrid to the power circuit at a point operative to cause charging currentin the resistor to bias the grid negatively relative to the cathode tomaintain the gas tube non-conducting while the storage means is chargingand to fire the gas tube when the charge in the storage means ismaximum.

6. In combination, an alternating-current power source; a powertransformer having a primary winding and a secondary winding possessingsubstantial leakage inductance; means connecting the primary winding tothe power source; a charge storage device; a pulse transformer havingprimary and secondary windings; resistance means; means connecting thestorage device, the primary of the pulse transformer and the resistancemeans in a closed series connection in the order named with thesecondary winding of the power transformer to form a circuitsubstantially resonant at the frequency of the power source; load meansconnected to the secondary winding of the pulse transformer; agrid-controlled, gas-filled rectifier tube having a cathode, an anode,and a, grid; means connecting the anode of the gas tube to the junctionof the storage means and the secondary winding of the power transformer;means connecting the cathode of the gas tube to the junc- I tion of theresistance means and the primary winding of the pulse transformer; andmeans connecting the grid of the gas tube to the junction of theresistance means and the secondary winding of the power transformer.

MYRON G. PAWLEY.

No references cited.

